Lassen Volcanic National Park features Lassen Peak, the largest plug dome volcano in the world. The area surrounding Lassen Peak is still volcanically active with boiling mud pots, hot springs, and fumaroles. Sulphur Works geothermal area is just off the scenic highway through the park and is basically a mini-Yellowstone. Lassen Peak had a series of small eruptions between 1914 and 1921, and is currently being monitored for volcanic activity. The western part of the park features mountains created by lava flow called lava pinnacles.